The invention relates to a pierce nut, and in particular, to a pierce nut, which can ensure a high joining strength even when applied to a metallic plate, to which a large amount of oil adheres.
In place of weld nuts, which necessitate a weld equipment and involve problems of poor positional accuracy and failure of clamping caused by spreading of sputter, pierce nuts simply applicable to a metallic plate such as aluminum plate, steel plate and the like have been recently used widely. More specifically, pierce nuts ensure a desired joining strength as the result of striking a nut itself into a metallic plate set on an exclusive lower die from above by means of a pressing tool such as punch or the like causing an inner cylindrical portion of the nut to form a hole at a predetermined position of the metallic plate, to which the pierce nut is applied, at the time of such striking, and using the lower die to cause plastic flow of a portion near the hole of the metallic plate, into a recess formed between the inner cylindrical portion of the nut and an outer cylindrical portion of the nut to cause the portion to bite into the recess.
FIG. 8 is a view illustrating a state, in which a conventional pierce nut is struck into a metallic plate, to which an oil adheres. The pierce nut comprises an inner cylindrical portion 2 provided centrally on an underside of a main nut body 1 (Its wall is parallel to an axis. Its inner space is contiguous to a center of an upper surface of the nut. Its inner surface is formed with a female thread, which functions as a nut.), an outer cylindrical portion 4 (Its wall portion is normally tapered as if its top were disposed on a point on an axis but suffices to be shaped to be capable of preventing the metallic plate having undergone plastic flow from being drawn out), and a recess 5 formed between an outer surface of the inner cylindrical portion and an inner surface of the outer cylindrical portion. When the pierce nut of such construction is struck into a metallic-plate 8, to which an oil adheres (Concretely, the metallic plate is placed on a projection 10 of a lower die 9, and the pierce nut placed on the metallic plate so that a central axis of the pierce nut coincides with that of the lower die is pressed against the metallic plate by means of a pressing tool such as a punch or the like. As a result, the metallic plate is punched out by the inner cylindrical portion of the pierce nut to be formed with a hole, a diameter of which corresponds with an outer diameter of the inner cylindrical portion of the pierce nut. When the pierce nut is further pressed toward the lower die, the projection of the die exerts pressure on a peripheral edge portion of the hole of the metallic plate, the portion is caused to undergo plastic flow to be pushed deep into the recess of the pierce nut, and eventually the metallic plate thus pushed is caused to make caulking and joining through the recess of the pierce nut.), the striking action causes an oil flowing into the recess to be confined in the portion to form a puddle of oil 7, so that the metallic plate, which should have been filled deep into the recess, that is, the oil puddle forming portion due to plastic flow, cannot reach the recess deep, and there is resulted a disadvantage that a state, in which the metallic plate is joined to the pierce nut, becomes incomplete (Concretely, a clinching force, that is, a force for preventing the pierce nut from being axially drawn out, and the slipping torque, that is, a force for preventing the pierce nut from rotation about its axis are exceedingly reduced).
Accordingly, in the case where a pierce nut is to be struck into a metallic plate, to which a large amount of oil adheres, there is caused a problem that a worker must beforehand perform a preliminary work such as wiping-off or air-blowing of an oil adhered to the metallic plate, which not only imposes surplus load on the worker but also incurs lowering of working efficiency and hence an increase in cost.
The invention has been contemplated to solve the above-mentioned problems of the prior art and to provide a pierce nut which can ensure a high joining strength equivalent to that of the prior art even when applied to a metallic plate, to which a large amount of oil adheres.
More specifically, a pierce nut according to the invention has an inner cylindrical portion 2 provided centrally on an underside of a main nut body 1 and formed at an inner surface thereof with a female thread 3, an outer cylindrical portion 4 provided on a peripheral edge of an underside of the main nut body, and a recess 5 defined by an outer surface of the inner cylindrical portion and an inner surface of the outer cylindrical portion, and characterized in that at least one passage 6 is provided to communicate between the recess and an outer surface of the pierce nut to enable flowing of a fluid.